1. Field of the Invention
The present invention relates to an ultraviolet irradiation water treatment apparatus which irradiates water with an ultraviolet ray to inactivate or detoxify algae, microbes, pathogenic protozoa, and the like in a water-purifying treatment, a sewage treatment, a food effluent treatment, a chemical effluent treatment, a deep-sea vessel ballast water treatment, and the like, for example, and to an ultraviolet irradiation water treatment apparatus of high ultraviolet irradiation efficiency.
2. Description of the Related Art
Conventionally, waterworks in Japan are managed based on sanitarian safety by chlorination.
Recently, water system contamination problems have been generated by new and reconstructed pathogenic microbes such as cryptosporidium and Giardia. There are also the problems of mass generation of algae with the progress of eutrophication, which is organic matter pollution, in lakes, dams, and rivers, which are water service resources. The mass generation of algae causes an unusual odor and taste, discoloring, aggregation, sedimentation inhibition, filter clogging, and filtrate water leakage problems. Additionally, a chlorine agent injected for the purpose of disinfection reacts with the organic matter in raw water to produce toxic by-products such as trihalomethane.
The improvement in management of a basic pattern in which the aggregation, filtration, and chlorination are sequentially performed is being studied to solve these problems for conventional waterworks in Japan.
Specifically, use of ultraviolet disinfection, in which water is irradiated with an ultraviolet ray, is now replacing the conventional chlorination method. In ultraviolet disinfection, disadvantageously complicated chemical injection control is not required, and no toxic by-products such as trihalomethane are not generated. Ultraviolet disinfection is also highly effective at suppressing the proliferation of cryptosporidium, which reduces infectability thereof. Therefore, sometimes an ultraviolet irradiation treatment is performed to oxidize and disinfect residue organics at water purification works.
In ultraviolet disinfection, usually, filtered water or aggregated and sedimented water is irradiated, as this provides high ultraviolet transmission efficiency. However, sometimes the raw water is irradiated with an ultraviolet ray in order to improve the aggregation or to eliminate the infectability of pathogenic protozoa such as cryptosporidium. That is, the raw water is irradiated with an ultraviolet ray instead of use of prechlorination.
Ultraviolet irradiation also effectively prevents the reproduction of algae, which is desired in the water-purifying treatment.
Where ultraviolet irradiation is used to kill pathogenic microbes or protozoa, ultraviolet in the wavelength range of 200 nm to 300 nm, which is called the UV-C band, is effective. A low-pressure or medium-pressure mercury lamp in which mercury vapor is enclosed in a lamp is used to generate a UV-C band ultraviolet ray.
An apparatus in which one or plural ultraviolet lamps are disposed in parallel is well known as an apparatus for irradiating water with an ultraviolet ray (see “ULTRAVIOLET DISINFECTION GUIDANCE MANUAL”, United States Environmental Protection Agency, June 2003, Draft).
However, the ultraviolet irradiation dose necessary to inactivate pathogenic protozoa, microbes, and virus, which are disinfection targets, depends on the microbial species in question. Therefore, it is necessary for the water containing the pathogenic protozoa, bacteria, and virus, which are the disinfection targets, to be effectively irradiated with an ultraviolet ray within the period of time the water is present in the ultraviolet irradiation water treatment apparatus.
Since the intensity of an ultraviolet ray is decreased in inverse proportion to the square of the distance from the ultraviolet lamp, in order to effectively irradiate the water with the ultraviolet ray, it is necessary to cause the water to pass near the ultraviolet lamp.
Therefore, Jpn. Pat. Appln. KOKAI Publication No. 9-503160 discloses a method in which a spiral guide vane is disposed in order that the water flows while swirling in an outer periphery of the ultraviolet lamp, and Jpn. Pat. Appln. KOKAI Publication Nos. 2004-512905 and 2001-516637 disclose a method in which a secondary flow, such as a vortex flow, is induced such that the whole body of water passes near the ultraviolet lamp.
The configuration shown in FIG. 41 can be cited as an example of a conventional ultraviolet irradiation water treatment apparatus 100.
In the ultraviolet irradiation water treatment apparatus 100, water W1 enters from a water inlet pipe 102 located in a lower portion of a cylindrical vessel 101, and the water W1 rises in an axial direction of the vessel 101. Then, the water W1 flows out from a water outlet pipe 103 located in an upper portion of the vessel 101. An ultraviolet lamp 105 surrounded by a protective tube 104 is disposed along a central axis of the cylindrical vessel 101. A spiral guide vane 106 is disposed in the vessel 101. In an ultraviolet irradiation water treatment apparatus 100 having the above-described configuration, the water W1 flows while swirling around the ultraviolet lamp 105 along the spiral guide vane 106. Therefore, the whole body of water W1 can evenly be irradiated with the ultraviolet ray.
The configuration shown in FIG. 42 can be cited as another example of a conventional ultraviolet irradiation water treatment apparatus, 100S. In FIG. 42, the same components as those in FIG. 41 are designated by the same numerals, and an overlapping description is omitted.
In the ultraviolet irradiation water treatment apparatus 100S, the water W1 flows in from the water inlet pipe 102 formed in the lower portion of the cylindrical vessel 101, and the water W1 rises in the axial direction of the vessel 101. Then, the water W1 flows out from the water outlet pipe 103 formed in the upper portion of the vessel 101. The ultraviolet lamp 105 surrounded by the protective tube 104 is disposed in the central axis of the cylindrical vessel 101. A spiral flow path 110 having a semicircular shape in section is formed in an inner wall surface of the cylindrical vessel 101 so as to surround the ultraviolet lamp 105. That is, in the ultraviolet irradiation water treatment apparatus 100S having the configuration shown in FIG. 42, the water W1 flows in from the water inlet pipe 102, and the water W1 passes through the spiral flow path 110. This enables the water W1 to flow while swirling in the outer periphery of the ultraviolet lamp 105. Therefore, the whole body of water W1 can evenly be irradiated with an ultraviolet ray. Because the spiral flow path 110 has a semicircular shape in section, a vortex flow is induced as a secondary flow of the fluid. Therefore, the water W1 passes near the ultraviolet lamp 105, and the water W1 can efficiently be irradiated with an ultraviolet ray.
However, there are the following problems in the conventional ultraviolet irradiation water treatment apparatus.
(A) In the case where plural ultraviolet lamps are used to treat a large amount of water, the structure of the apparatus necessarily becomes more complicated, which could increase the risk of failure. Additionally, the production cost is high since the apparatus has a complicated structure.
(B) In order to treat a large amount of water, it has also been considered to dispose plural ultraviolet lamps in parallel with the direction in which the water flows. However, in the case where plural ultraviolet lamps are disposed, and one of the lamps has broken, the neighborhood of the broken ultraviolet lamp is insufficiently irradiated with ultraviolet rays, since the ultraviolet rays from the surrounding ultraviolet lamps are blocked by the broken ultraviolet lamp.
(C) Crystal quartz or synthetic quartz is used as a material for the protective tube which is disposed to protect the ultraviolet lamp. The crystal quartz or synthetic quartz glass tube is highly fragile, and easily breaks if subjected to slight impact. Therefore, in the case where an ultraviolet lamp is broken, unfortunately, mercury enclosed in the ultraviolet lamp leaks into the water, or fragments of the quartz glass tube constituting the ultraviolet lamp and protective tube are mixed into the water.